dissolve

A transition between two shots, where one shot fades away and simultaneously another shot fades in. Dissolves are done at the lab in the printing phase, but prepared by the negative cutter, who cuts in an overlap of the two shots into the A&B rolls. Labs will only do dissolves in fixed amounts, such as 24 frames, 48 frames, etc.

Glossary of Film Terms - http://homepage.newschool.edu/~schlemoj/film_courses/glossary_of_film_terms/
reprinted with permission

To separate into competent parts; to disorganize; to break up; hence, to bring to an end by separating the parts, sundering a relation, etc.; to terminate; to destroy; to deprive of force; as, to dissolve a partnership; to dissolve Parliament.

Lest his ungoverned rage dissolve the life.
Shak.

2.

To break the continuity of; to disconnect; to disunite; to sunder; to loosen; to undo; to separate.

Nothing can dissolve us.
Shak.

Down fell the duke, his joints dissolved asunder.
Fairfax.

For one people to dissolve the political bands which have connected them with another.
The Declaration of Independence.

3.

To convert into a liquid by means of heat, moisture, etc.,; to melt; to liquefy; to soften.